Hi. This has happened to me twice now: after playing Spotify via Bluetooth for a while (about half an hour) with the volume off through the PA, when I raise the fader, the music sounds slower and bassier, like when you convert audio directly from 48kHz to 44.1kHz. To fix it, I have to disconnect Bluetooth from my smartphone (Google Pixel 8) and reconnect it.
I haven’t seen anyone else experiencing this, so it might be something related to my smartphone.